This invention relates to a propulsion and stabilization system for an inductive repulsive type, magnetically levitated vehicle, and more specifically, to a magnetically levitated ("maglev") vehicle which is levitated and guided by figure eight-shaped null-flux coils.
Maglev development began more than two decades ago in the United States, Germany, Japan, Canada and England. In the United States, renewed interest has been directed toward magnetic levitation transportation systems in view of such factors as energy conservation, high speed transportation at ground level, economic and environmental problems associated with conventional systems and competition from Germany and Japan.
The use of electrodynamic levitation in maglev systems is well known in the prior art (see U.S. Pat. No. 3,470,828, issued Oct. 7, 1969, to Powell et al.). A number of methods of using magnetic forces to suspend, guide, and propel vehicles have been described in the literature, of which there are two basic suspension concepts: one, called Electromagnetic System ("EMS"), utilizes the attractive force between controlled d.c. electromagnets and ferromagnetic rails, while the other, called the Electrodynamic System ("EDS"), utilizes the repulsive force between eddy currents induced in non-ferromagnetic metal conductors and superconducting magnets ("SCM's"). Generally, the SCM's are mounted on the lower part of the vehicle, while the iron rails or non-ferromagnetic metal conductors are mounted on a fixed guideway.
A special suspension concept based on EDS is called "null flux" suspension. It was invented by J. Powell and G. Danby in the late sixties and patented in 1969, see U.S. Pat. No. 3,470,828 referenced above. The concept was invented as a way to reduce the electromagnetic drag force that is inherent in any suspension system that relies on eddy currents in the conductors. The concept also results in a stiffer suspension system than non-null-flux approaches. The heart of the null-flux system is a series of shorted "FIG.-8" coils that may be vertically oriented on the guideway or folded over so that the upper and lower loops are parallel to each other.
When an energized coil, like a SCM, passes midway between the loops, no net current is induced in the loops because they are cross connected or counter wound, hence the term "null-flux". When the SCM is displaced from the midplane or neutral position relative to the upper and lower loops, a large net current is induced in the loops and a strong repulsive force acts to restore the SCM to the neutral or null-flux position.
In 1967-8 the feasibility of using Powell and Danby's concept for the suspension and guidance of a Mach 10 rocket sled was evaluated. At that time, continuous sheets of aluminum in place of guideway coils was proposed, a concept that was extended to high-speed ground transportation systems by Howard Coffey and Frank Chilton. In 1970 H. H Kolm and R. D. Thorton conceived a novel form of maglev in which saddle-shaped SCM's were placed along the bottom of the vehicle. This system provided levitation, guidance and propulsion.
J. K. Dukowicz, L. O. Hoppie and T. C. Wang developed a system that combined levitation, propulsion and guidance of a vehicle over a guideway consisting of metallic loops, which did not require three-phase excitation.
The most sustained efforts in developing the EDS system have been made in Japan. A series of test and developmental vehicles have been constructed under the sponsorship of Japanese National Railroads and later the Railway Technical Research Institute. The EDS system in Japan uses SCM's on the vehicle, which reacts against conducting coils in the guideway to achieve levitation, guidance and propulsion. The SCM's are located vertically, reacting with the figure-eight shaped null-flux coils on the guideway for levitation and guidance.
The development of the EMS systems can be traced back to 1969, when Krauss-Maffei (KM) and Messerschmitt-Boelkow-Blohm (MBB) began development of two systems. KM's system used separate levitation and guidance systems, while KM used a combined levitation/guidance system. In the United States, research on EMS systems began in 1970 when both top-suspended and bottom-suspended systems were constructed.
Some maglev design concepts utilize the same vehicle magnets to perform more than one of the basic functions of suspension, guidance or propulsion, as provided above. The updated Japanese EDS maglev system uses a combined propulsion and null-flux suspension concept in which two rows of figure-eight-shaped null-flux coils mounted on the side walls of the box-shaped guideway are cross connected. This arrangement requires only one set of guideway coils to perform three functions. An analysis of the Japanese system is set forth in the applicants' recently published Performance Analysis of the Combined EDS Maglev Propulsion, Levitation, and Guidance System, The International Conference on Speedup Technology for Railway and Maglev Vehicles, (November 1993) and Study of Japanese Electrodynamic Suspension Maglev System, Center for Transportation Research, Argonne National Laboratory (April 1994).
In the invention described herein, the SCM's coupled to the vehicle's dual keels interact with two mirror image rows of null-flux coils mounted to the vertical walls of the guideway slots to produce a form of null-flux suspension, lateral guidance, and, when the coils are cross-connected and energized by an external multi-phase power source, propulsion.